[{"_id":ObjectId("543fa67e9672ec37ebe3d026"),"name":"Alice","images":[{url:"http://images.com/1.jpg"},{url:"http://images.com/2.jpg"},{url:"http://images.com/3.jpg"},]},{"_id":ObjectId("543fa67e9672ec37ebe3d027"),"name":"Bob","images":[{url:"http://images.com/4.jpg"},{url:"http://images.com/5.jpg"},]},]

db.collection.find({},{_id:0,name:1,images:{$size:"$images"}})